Conventionally, a planar lighting device using a cold cathode fluorescent tube as a light source is widely used as a backlight illumination in a liquid crystal display device using a liquid crystal display panel. The cold cathode fluorescent tube used therein utilizes light emission of a phosphor (fluorescent material), and has a restriction in a displayable color reproduction range. Therefore, various examinations have been carried out for reproducing a further clear and natural tone. Above all, the planar lighting device for backlight using a light emitting diode (an LED element) of three colors such as red light (R-light), green light (G-light), and blue light (B-light) is focused. The light source using the three colors of R-light, G-light, and B-light or a multi-color LED element has a wider color reproduction range than that of the cold cathode fluorescent tube, thus making it possible to obtain a high image quality. Alternately, it is also possible to display an image by a field sequential method. Therefore, such developments are actively promoted.
In addition, one configuration has been illustrated, which suppresses a heat generation increasing as a drive current increases by using a semiconductor laser element as a light emitting element of at least one of the three color light emitting elements so as to reduce a fluctuation of the characteristics. The semiconductor laser element has a luminance higher than that of the LED element and is suitable for higher output. Note that this configuration example specifically shows that a red color semiconductor laser is used (see Patent Document 1, for example).
As Patent Document 1 describes in its example, when a laser is used as a light source, it is important to realize a uniform luminance over a large area. If there is a variation in luminance, it extremely deteriorates the image displayed thereon even when its color reproduction range gets wider. However, almost no configuration example that uses a laser light source as a backlight illumination exists. Patent Document 1 neither teaches nor indicates any strategy to realize the uniform luminance.
Meanwhile, the conventional liquid crystal display device has two polarizing plates. In general, the two polarizing plates are provided in front and back ends of a liquid crystal display panel so that the liquid crystal display panel may be sandwiched by the two polarizing plates. The two polarizing plates are arranged such that the two polarizing plates may be substantially parallel to one another, and a prescribed intersection angle may be formed by the polarization axes of the two polarizing plates. Here, the “intersection angle” is an angle formed by the polarization axes of the two polarizing plates when viewing the two polarizing plates disposed substantially parallel from a direction vertical to their major surfaces. Therefore, the conventional liquid crystal display device has a problem that 50% or more of natural light for illumination from the LED of the backlight lighting device or the cold cathode fluorescent lamp are lost. It significantly lowers the efficiency in its use of light. To overcome such a problem, for example, if the polarizing plate on the back side of the liquid crystal display panel in the liquid crystal display device is omitted, the light use efficiency can be drastically improved. However, for now, there has been no document released which discloses the liquid crystal display device using the planar lighting device as the backlight lighting device without a polarizing plate on the back side of the liquid crystal display panel to improve the light use efficiency.
Patent document 1: JP 2005-064163 A